As one of driving devices for driving an auxiliary machine of an automobile, a belt type auxiliary machine driving device (belt transmission device) has been conventionally known which transmits engine's rotation to the auxiliary machine through a belt. A V-ribbed belt is used in general as the transmission belt in view of the transmission power, lifetime, and the like. In the V-ribbed belt, a plurality of ribs extending in the longitudinal direction of the belt are formed so as to be arranged in the widthwise direction of the belt at a predetermined pitch on the lower face (the inner peripheral face) of the belt body. Core wires are embedded in the belt body at a predetermined pitch in the widthwise direction of the belt.
In belt-type auxiliary machine driving devices using such a V-ribbed belt, in general, pulleys to which the V-ribbed belt is wound includes misalignment, such as offset, slant, and the like, and strictly, the belt would approach and enter into a pulley with inclination, as shown in FIG. 11, for example. When the entrance angle of the belt to a V-ribbed pulley is large, noise is liable to be generated due to slip of the ribbed surface of the belt over the groove face of the pulley in belt running.
To tackling this problem, in the drive system composed of V-ribbed pulleys as shown in FIG. 11, the entrance angle of the V-ribbed belt is calculated geometrically from maximum misalignment (a offset amount, a slant angle, and the like) of the pulleys at the stage of pulley layout design to check whether the calculated entrance angle is an angle at which the belt generates noise in belt running, and the positions of the pulleys are modified if necessary.
Besides the above method in which the entrance angle is obtained and the layout is modified in advance at the design stage, another method for preventing noise generated due to pulley misalignment has been known, as disclosed in Patent Document 1, for example. Namely, the side pressure is measured by a strain gauge arranged at the side face of the groove of a pulley to detect pulley misalignment and the arrangement of the pulleys is corrected on the basis of the detect misalignment.
Patent Document 1: Japanese Patent Application Laid Open Publication No. 2002-349649A